Device for protecting a geotechnical or geophysical probe

ABSTRACT

A device ( 1 ) for protecting a geotechnical or geophysical probe ( 13 ) having an elongated shape and capable of undergoing radial deformation, includes: a plurality of flexible members ( 2 ) having an elongated shape and capable of undergoing radial deformation in a functional configuration of the device ( 1 ); elements for the longitudinal compensation of the radial deformation of the flexible members ( 2 ) in a functional configuration of the device ( 1 ); two flexible member bearings ( 301, 302 ) each receiving an end of the flexible members ( 2 ), the bearings ( 301, 302 ) being capable of longitudinal movement on the probe ( 13 ) so that the flexible members ( 2 ) longitudinally protect the outer portion of the probe ( 13 ) between the bearings ( 301, 302 ) in a functional configuration of the device ( 1 ).

The present invention relates to a device for protecting elongate-shapedgeotechnical or geophysical probes, in particular probes able to deformradially. It also concerns a probe covered with such a device.

Various types of probe are known for determining the characteristics ofa soil. Geotechnical probes are used for determining the technicalcharacteristics of a soil, such as for example the mechanical strength.Geophysical probes are also used for evaluating the physical andchemical characteristics of soils.

One well known type of geotechnical probe is the probe for a pressuremeter. A pressure meter is an apparatus that measures in situ thecharacteristics of resistance and deformability of a soil. It consistsof a radially expandable three-cell cylindrical probe, a set ofpressurisation and pneumatic regulation components, and a volumecontroller. This apparatus makes it possible to know the increase involume of a drilling slice according to the pressures applied.

These pressure meters have been well known to persons skilled in the artsince their invention by L Ménard in 1955. They are in particulardescribed in the application FR 1 117 983.

Since then devices for protecting these probes have been developed, inorder to protect the probes when they are disposed in cohesion-lacking,gravelly or fractured soils.

Thus a probe protection device is known consisting of a flexible tubeprovided with slots, as described in the applications FR 1 234 756 andFR 2 702 565. A device consisting of two half-tubes provided with slotsis also known.

However, when the probe expands, very high stresses develop at the endsof the slots, which may lead to a plastic deformation causing anirreversible widening of the slots.

Disposing metal blades on a rubber sheath or a frame composed of springsembedded in a layer of plastics material as described in the applicationEP 0 146 324 is also known.

Such a device is however very rigid, which interferes with thepressure-measurement tests.

The invention proposes a device for protecting a geotechnical orgeophysical probe, and in particular a pressure-measuring probe,remedying these drawbacks.

In particular, the invention proposes a device for protecting the probein hard cutting soils, adapted to high expansion of the probe cells, andwhich does not impair the measurement of the deformation of the probe.In particular, the protection device according to the invention has noinertia vis-à-vis the probe.

The subject matter of the invention is thus a device for protecting ageotechnical or geophysical probe, the probe being elongate in shape andable to deform radially. The device according to the inventioncomprises:

-   -   a plurality of elongate-shaped flexible elements, able to        undergo radial deformation, in the operational configuration of        the device,    -   means of longitudinal compensation for the radial deformation of        the flexible elements, in the operational configuration of the        device,    -   two flexible-element supports, each accepting one end of the        flexible elements, the supports being able to move        longitudinally on the probe,

so that the flexible elements longitudinally protect the external partof the probe lying between said supports, in the operationalconfiguration of the device.

The means for longitudinal compensation of the radial deformation of theflexible elements advantageously consist of an interstice in at leastone of the flexible-element supports and a curved end of the flexibleelements, each end being disposed in reversible sliding in saidinterstice.

To facilitate the acceptance of the ends of the flexible elements, theinterstice is preferable delimited by two annular zones with differentdiameters.

The means for longitudinal compensation of the radial deformation of theflexible elements preferably also comprise at least one damper intendedto damp the longitudinal movements of at least one of theflexible-element supports, in the operational configuration of thedevice. The presence of these dampers optimises the longitudinalcompensation for the radial deformation of the flexible elements andreduces the inertia of the probe protection device.

In another embodiment, the flexible elements are fixed to theflexible-element supports, and the means of longitudinal compensationfor the radial deformation of the flexible elements comprise at leastone damper intended to damp longitudinal movements of at least one ofthe flexible-element supports, in the operational configuration of thedevice.

The dampers used in the device according to the invention can be of anynature. It is possible in particular to use springs, or elements madefrom elastic material, such as polyurethane. The dampers can inparticular be elastic rings.

In order to adapt well to the currently used geotechnical andgeophysical probes, which are generally cylindrical in shape, theflexible element supports are preferably cylindrical in shape. Tofacilitate their assembly on the probe, the flexible-element supportscomprise a plurality of cylinder portions assembled together. It is inparticular possible to use two half cylinders or four quarter cylinders.

The flexible elements can be produced from any flexible material, and inparticular a material able to completely resume its shape after havinglost it by deformation during the radial deformation of the probe.

The flexible elements are preferably steel blades, and in particularmade from stainless steel. The flexibility of the blade will be chosenaccording to the envisaged deformation of the blade during geotechnicalor geophysical tests.

Another subject matter of the invention is a geotechnical or geophysicalprobe covered with a protection device described above.

The device is particularly suitable for the protection ofpressure-measurement probes, in particular of the type comprising threeinflatable sleeves aligned along the longitudinal axis of the probe.

In this case, the flexible element supports are preferably disposed oneach side of the assembly formed by the three inflatable sleeves, foroptimum protection of the probe.

When the device comprises a damper intended to damp the longitudinalmovements of at least one of the flexible-element supports, eachflexible-element support is advantageously able to move longitudinallybetween two stops of the probe, the movement being damped by the damper.

Other aims, features and advantages of the invention will emerge from areading of the following description, given solely by way of example,and made with reference to the accompanying drawings, in which:

FIG. 1 is a view in perspective of a part of an end of a protectiondevice according to the invention,

FIG. 2 is a view in partial and divided longitudinal section of part ofa pressure-measurement probe according to the invention, before radialdeformation of the probe, and

FIG. 3 is a view in partial and divided longitudinal section of part ofa pressure measurement probe according to the invention, expandedradially during a pressure-measurement test.

The protection device 1 according to the invention comprises a pluralityof flexible elements 2, disposed at each of their ends in aflexible-element support 3.

The flexible elements 2 are stainless steel blades. Each flexibleelement 2 is curved at its end, for example by a fold.

Each flexible-element support 3, which accepts an end of the flexibleelements 2, consist of two semi-cylindrical half-supports 4, only one ofwhich has been shown in FIG. 1. The two half-supports 4 are connectedtogether by means of screws, not shown, disposed in threaded holes 6.Each half-support 4 comprises a half-support body 8 onto which anannular element 5 is screwed by means of screws 7.

The half-support body 8 comprises an annular zone 9 that is extended bya shoulder 10 onto which the annular element 5 is screwed.

The annular element 5 and the annular zone 9 of the half-support body 8,which have different diameters, delimit an interstice 11 in which theends of the flexible elements 2 are disposed.

The half-support 4 is advantageously provided with a pin 12 at each endof the half-support 4. The pins 12 hold the two flexible elements 2situated at the ends of the half-support 4, which makes it possible tohold all the flexible elements 2 in the half-support 4. To accept thepin 12, the ends of the flexible elements 2 can be in the form of forks.

The other end of the flexible elements 2 is disposed in an identicalmanner in the same flexible element support 3.

FIG. 2 illustrates a pressure-measurement probe 13 covered with theprotection device 1, before a pressure-measurement test.

The pressure-measurement probe 13 comprises a central probe body 12intended to supply a zone 15 adjacent to the probe body 12 with liquidand gas, by means of a gas supply duct 14, provided in a solid zone ofthe probe body 12, and a liquid supply duct 26. The liquid supply duct26 is intended to supply a central inflatable sleeve, and the gas supplyduct 14 is intended to supply two inflatable sleeves adjacent to thecentral sleeve, the three sleeves being placed in the zone 15.

The probe 13 is also provided with a shoe 27 at its bottom end, in theoperational configuration of the probe 13.

The adjacent inflatable sleeves are supplied with gas by means of ducts16 and 17 that connect the gas supply duct 14 to the adjacent inflatablesleeves.

The pressure-measurement probe 13 is covered with the protection device1 described above. The device comprises, on each side of the zone 15,two flexible element supports 301, 302, each support 301, 302 consistingof two semi-cylindrical half supports. The half supports comprise a halfsupport body 801, 802 to which an annular element 501, 502 is fixed bymeans of screws 701, 702. Flexible elements 2, which are stainless steelblades folded at their ends, are disposed in the interstice delimited bythe half support bodies 801, 802 and the annular elements 501, 502.

The flexible-element support 301 disposed at the top end of theprotection device 1 of the probe 13, in the operational configuration ofthe probe 13, is able to move longitudinally between two stops 18, 19,the stop 18 being the called the external stop, and the stop 19 beingcalled the internal stop. At rest, the half-support body 801 is heldagainst the external stop 18 by means of a damper 20. The damper 20 is apolyurethane ring.

Likewise, at the bottom end of the probe protection device 13, in theoperation configuration of the probe 13, the flexible-element support302 is able to move longitudinally between two stops 21, 22 of the shoe27, the stop 22 being called the external stop, and the stop beingcalled the internal stop. At rest, the half-support body 802 is heldagainst the external stop 22 by means of a damper 24. The damper 24 is apolyurethane ring.

FIG. 3, where the identical elements bear the same reference signs,illustrates the probe 13 during the pressure-measurement test. Thecentral inflatable sleeve 23, and the inflatable sleeves 24, 25 adjacentto the central sleeve 23, are supplied with fluid and are therefore inthe inflated state. For more clarity, the sleeves 23, 24, 25 are shownschematically. This expansion of the sleeves 23, 24, 25 causes a radialdeformation of the flexible elements 2. The deformation simultaneouslycauses a longitudinal movement of the two supports 301, 302 in thedirection of the internal stops 19, 21.

Thus the top 301 and bottom 302 flexible-element supports which, beforethe expansion of the sleeves 23, 24, 25, were in abutment on theexternal stops 18, 22, will bear on the internal stops 19, 21, when thesleeves 23, 24, 25 are inflated.

The radial deformation of the flexible elements 2 is also accompanied bywithdrawal by sliding of the ends of the flexible elements 2 into theinterstices delimited by the half-support bodies 801, 802 and theannular elements 501, 502. Thus, during the radial deformation, thecurved ends of the flexible elements 2 slide in the interstices and moveaway from the bottom of the interstices, which reduces the inertia ofthe device 1.

Conversely, at the end of the pressure-measurement test, during thedeflation of the sleeves 23, 24, 25, the radial deformation of theflexible elements 2 diminishes. The flexible-element supports 301, 302regain their initial position against the external stops 18, 22 underthe action of the dampers 20, 24. At the same time, the flexibleelements 2 also regain their initial position by sliding of their endsin the interstices, the sliding taking place in the direction of thebottom of the interstices.

Even if FIGS. 2 and 3 show a protection device 1 comprising both a firstcompensation means comprising flexible elements 2 provided with curvedends disposed in interstices, and a second compensation means comprisingdampers 20, 24 able damp longitudinal movements of the supports 301,302, the protection device 1 may comprise only the first or secondcompensation means.

The device 1 according to the invention therefore effectively protectsthe probe 13, without impairing measurements during thepressure-measurement test, by virtue of the low resistance of the device1 to the deformation of the probe 13.

1. Device (1) for protecting an elongate-shaped geotechnical orgeophysical probe (13) and able to deform radially, characterised inthat it comprises: a plurality of elongate-shaped flexible elements (2),able to undergo radial deformation, in the operational configuration ofthe device (1), means of longitudinal compensation for the radialdeformation of the flexible elements (2), in the operationalconfiguration of the device (1), two flexible-element supports (301,302), each accepting one end of the flexible elements (2), the supports(301, 302) being able to move longitudinally on the probe (13), so thatthe flexible elements (2) longitudinally protect the external part ofthe probe (13) lying between said supports (301, 302), in theoperational configuration of the device (1).
 2. Device (1) according toclaim 1, characterised in that the means of longitudinal compensationfor the radial deformation of the flexible elements (2) are formed by aninterstice (11) in at least one of the flexible-element supports (301,302) and by a curved end of the flexible elements (2), each end beingdisposed for reversible sliding in said interstice (11).
 3. Device (1)according to claim 2, characterised in that the interstice (11) isdelimited by two annular zones (5, 9) with different diameters. 4.Device (1) according to claim 2, characterised in that the means oflongitudinal compensation for the radial deformation of the flexibleelements also comprise at least one damper (20, 24) intended to damplongitudinal movements of at least one of the flexible-element supports(301, 302), in the operational configuration of the device (1). 5.Device (1) according to claim 1, characterised in that the flexibleelements (2) are fixed to the flexible-element supports (301, 302), andin that the means of longitudinal compensation for the radialdeformation of the flexible elements comprise at least one damper (20,24) intended to damp longitudinal movements of at least one of theflexible-element supports (301, 302), in the operational configurationof the device (1).
 6. Device (1) according to claim 4, characterised inthat the dampers (20, 24) are elastic rings.
 7. Device (1) according toclaim 1, characterised in that the flexible-element supports (301, 302)are cylindrical in shape and comprise a plurality of cylindricalportions assembled together.
 8. Device (1) according to claim 1,characterised in that the flexible elements (2) are steel blades. 9.Geotechnical or geophysical probe (13), characterised in that it iscovered with a protection device (1) according to claim
 4. 10. Probe(13) according to claim 9, characterised in that it is of the typecomprising three inflatable sleeves (23, 24, 25) aligned along thelongitudinal axis of the probe (13).
 11. Probe (13) according to claim10, characterised in that the flexible-element supports (301, 302) aredisposed on each side of the assembly formed by the three inflatablesleeves (23, 24, 25).
 12. Probe (13) according to claim 9, characterisedin that each flexible-element support (301, 302) is able to be movedlongitudinally between two stops (18, 19, 21, 22) of the probe (13), themovement being damped by the damper (20, 24).
 13. Device (1) accordingto claim 2, characterised in that the means of longitudinal compensationfor the radial deformation of the flexible elements also comprise atleast one damper (20, 24) intended to damp longitudinal movements of atleast one of the flexible-element supports (301, 302), in theoperational configuration of the device (1).
 14. Device (1) according toclaim 5, characterised in that the dampers (20, 24) are elastic rings.15. Device (1) according to claim 4, characterised in that the dampers(20, 24) are elastic rings.
 16. Geotechnical or geophysical probe (13),characterised in that it is covered with a protection device (1)according to claim
 1. 17. Probe (13) according to claim 16,characterised in that it is of the type comprising three inflatablesleeves (23, 24, 25) aligned along the longitudinal axis of the probe(13).
 18. Geotechnical or geophysical probe (13), characterised in thatit is covered with a protection device (1) according to claim
 5. 19.Probe (13) according to claim 18, characterised in that eachflexible-element support (301, 302) is able to be moved longitudinallybetween two stops (18, 19, 21, 22) of the probe (13), the movement beingdamped by the damper (20, 24).